1. Technical Field
Embodiments of the present invention relate to an insulating member, metal base substrate, and semiconductor module, and to manufacturing methods thereof.
2. Related Art
Semiconductor modules used in power supply devices are applied over a wide range, from consumer instruments such as domestic air conditioners and refrigerators, to industrial instruments such as inverters and servo controllers. From the point of view of power consumption, a semiconductor module is mounted on a wiring substrate such as a metal base substrate or ceramic substrate. One or a plurality of circuit elements, such as a power semiconductor element, is mounted on the wiring substrate, a plastic case frame is affixed, and the semiconductor module is completed by being sealed with a silicon gel, an epoxy resin, or the like.
Also, in order to reduce manufacturing cost, a semiconductor module fully molded using a transfer molding method has been developed (see, for example, Japanese Patent Application No. JP-A-9-139461, Paragraph [0038], FIG. 1, and FIG. 18). With a fully molded semiconductor module, a lead frame and heat sink are immovably linked, and an electrical insulation thereof is ensured. FIGS. 4 to 6 show an example of a heretofore known fully molded semiconductor module 40.
In the example shown in FIG. 4, a plurality of circuit elements 46, such as power semiconductor elements or drive ICs, are mounted on a lead frame 47, and are connected to each other by a bonding wire 48. After the assembly is placed in a predetermined molding die, a fully molded semiconductor module 40a is completed by pouring a molding resin 49 into the molding die. In the example shown in FIG. 5, in addition to the configuration of the example shown in FIG. 4, a heat sink 50 is provided in a lower portion of the module. In the example shown in FIG. 6, a metal base substrate 60, formed by a metal foil 62 and a metal base 63 being affixed in advance to the front and rear surfaces of an insulating layer 61, is provided. The metal base substrate 60 combines the two functions of an insulating layer and a heat sink.
However, from the point of view of power consumption, the heretofore known fully molded semiconductor module has an application limit in the region of 200V, 50 A, and when current capacity exceeds 50 A, the power semiconductor element loss increases, and there is a problem in that the cooling property of the fully molded semiconductor module is insufficient. With a semiconductor module using a metal base substrate, it is possible to make the thickness of the insulating layer of the metal base substrate small at 100 to 150 μm, meaning that it is possible to reduce the heat resistance of the lower portion of the power semiconductor. Meanwhile, with the fully molded semiconductor module, it is necessary to make the thickness of the molding resin 300 μm or more in order to ensure the loadability of the molding resin, and the heat resistance increases.
In the example shown in FIG. 5, when making the thickness of the molding resin 49 in the lower portion of the module 200 μm or less, a space in which no molding resin 49 is loaded remains in, for example, a gap between the lead frame 47 and heat sink 50, and an insulation failure occurs. Although the loadability is improved by raising the resin injection pressure when molding, this may be a cause of a deformation or disconnection of the bonding wire 47.
In the example shown in FIG. 6, as the circuit element 46 and bonding wire 47 are joined directly to the metal base substrate 60, there is no need to load the molding resin in the lower portion of the module. However, as it is necessary to manufacture the metal base substrate 60 separately, there is a problem in that the cost of materials increases.
Also, in the insulating layer 61 of the metal base substrate 60, thermal conductivity is increased by loading an inorganic filler (for example, silicon oxide, aluminum oxide, silicon nitride, aluminum nitride, or boron nitride) into an epoxy resin, but as the breakdown voltage decreases along with an increase in the amount loaded, a thermal conductivity of 3 to 4 W/m·K is the limit, and there is a limit to the cooling property.
Although it is also possible to use a ceramic substrate, which is a sintered body of aluminum oxide, silicon nitride, aluminum nitride, or the like, for the wiring substrate in order to increase the thermal conductivity, there is a problem in that the ceramic substrate causes the cost to increase further than the metal base substrate.